Digging for Relics of the Past: The Ancient and Obscured Bulge Globular Cluster NGC 6256

Cadelano, Mario; Saracino, S.; Dalessandro, E.; Ferraro, F. R.; Lanzoni, B.; Massari, D.; Pallanca, Cristina; Salaris, Maurizio

doi:10.3847/1538-4357/ab88b3

Cited by 27 publications

(26 citation statements)

References 70 publications

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“…Figure 9 shows the age-metallicity distribution for the bulge GCs with available age estimate, where NGC 6440 is marked as a large red square. The data for the other clusters are mainly from Saracino et al (2019, see their Figure 16) and Oliveira et al (2020, see their Figure 12) with the addition of the recent age determination of NGC 6256 (Cadelano et al 2020). We also mark the age-metallicity of the oldest stellar population in the two Bulge Fossil Fragments (BFF; namely Terzan5 and Liller1) so far discovered into the bulge (Ferraro et al 2009b(Ferraro et al , 2016b(Ferraro et al , 2021.…”

Section: Discussionmentioning

confidence: 97%

A new identity card for the bulge globular cluster NGC 6440 from resolved star counts

Pallanca,

Lanzoni,

Ferraro

et al. 2021

Preprint

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We present a new identity card for the cluster NGC 6440 in the Galactic Bulge. We have used a combination of high-resolution Hubble Space Telescope images, wide-field ground-based observations performed with the ESO-FORS2, and the public survey catalog Pan-STARRS, to determine the gravitational center, projected density profile and structural parameters of this globular from resolved star counts. The new determination of the cluster center differs by ∼ 2 ′′ (corresponding to 0.08 pc) from the previous estimate, which was based on the surface brightness peak. The star density profile, extending out to 700 ′′ from the center and suitably decontaminated from the Galactic field contribution, is bestfitted by a King model with significantly larger concentration (c = 1.86 ± 0.06) and smaller core radius (r c = 6.4 ′′ ± 0.3 ′′ ) with respect to the literature values. By taking advantage of high-quality optical and near-infrared color-magnitude diagrams, we also estimated the cluster age, distance and reddening. The luminosity of the RGB-bump was also determined. This study indicates that the extinction coefficient in the bulge, in the direction of the cluster has a value (R V = 2.7) that is significantly smaller than that traditionally used for the Galaxy (R V = 3.1). The corresponding best-fit values of the age, distance and color excess of NGC 6440 are 13 Gyr, 8.3 kpc and E(B − V ) ∼ 1.27, respectively. These new determinations also allowed us to update the values of the central (t rc = 2.5 10 7 yr) and half-mass (t rh = 10 9 yr) relaxation times, suggesting that NGC 6440 is in a dynamically evolved stage.

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Section: Discussionmentioning

confidence: 97%

A new identity card for the bulge globular cluster NGC 6440 from resolved star counts

Pallanca,

Lanzoni,

Ferraro

et al. 2021

Preprint

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“…Comparing the ages we measure with those in the literature, there are only two clusters with extant age measurements: For NGC 6256, an isochrone-fitting analysis of photometry from the first-epoch HST imaging was recently presented by Cadelano et al (2020), who found an age of 13.0±0.6 using presumably identical Victoria-Regina isochrones but a different (maximum likelihood) fitting technique, in excellent agreement with our age of 12.9±1.0 Gyr (Table 3). Meanwhile, NGC 6342 is included in the relative age study by De Angeli et al (2005), who find a young relative age, consistent with our results.…”

Section: The Age-metallicity Relationmentioning

confidence: 95%

“…As an additional complication, distances from literature compilations, used to calculate orbital properties, can be unreliable as well, placing clusters on the wrong side of the Galactic bulge in some cases (e.g. Alonso-García et al 2015;Cadelano et al 2020). In addition, we know that not all MWGCs presently located in the inner Milky Way are confined to the Galactic bulge, instead showing a kinematic diversity including interlopers from the halo and thick disk (Ortolani et al 2019;Cadelano et al 2020;Pérez-Villegas et al 2020).…”

Section: Introductionmentioning

confidence: 99%

“…Alonso-García et al 2015;Cadelano et al 2020). In addition, we know that not all MWGCs presently located in the inner Milky Way are confined to the Galactic bulge, instead showing a kinematic diversity including interlopers from the halo and thick disk (Ortolani et al 2019;Cadelano et al 2020;Pérez-Villegas et al 2020). Therefore, placing inner Milky Way globulars on the MWGC age-metallicity relation is critical not only to determine progenitors or discriminate interlopers on a case-by-case basis, but also to constrain the global fraction of present-day MWGCs that were formed in situ (e.g.…”

Section: Introductionmentioning

confidence: 99%

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Relative Ages of Nine Inner Milky Way Globular Clusters from Proper Motion Cleaned Color-Magnitude Diagrams

Cohen,

Bellini,

Casagrande

et al. 2021

Preprint

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Our picture of the age-metallicity relation for Milky Way globular clusters (MWGCs) is still highly incomplete, and the majority of MWGCs lack self-consistent age measurements. Here, we exploit deep, homogenous multi-epoch Hubble Space Telescope (HST ) imaging of nine MWGCs located towards the inner Milky Way to measure their relative ages, in most cases for the first time. Our relative age measurements are designed to be directly comparable to the large set of MWGC ages presented by VandenBerg et al. 2013 (V13), using identical filters, evolutionary models, and bolometric corrections, extended to the higher extinction values relevant to our target clusters. Adopting the V13 MWGC age scale, our relative age measurements imply that our target clusters are consistently very old, with a mean age of 12.9±0.4 Gyr, with the exception of the young metal-rich MWGC NGC 6342. We perform two tests to validate the precision of our methodology, and discuss the implications of our target cluster loci in the MWGC age-metallicity plane. In addition, we use our fully self-consistent bolometric corrections to assess the systematic impact of variations in the total-to-selective extinction ratio R V on relative age measurements.

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“…This is a dense cluster (log ρ 0 ≈ 5.9 in units of M pc −3 ; Baumgardt & Hilker 2018) located in the Galactic bulge, at a distance of 6.8 kpc from the Sun (Cadelano et al 2020b) and characterized by a relatively low metal content compared to typical bulge GCs ([Fe/H]= −1.6; Vásquez et al 2018). In Cadelano et al (2020b), we applied a well-tested procedure (see Pallanca et al 2019Pallanca et al , 2021 to quantify the differential reddening affecting the cluster and we derived a high-resolution exctiction map (see Figure 3 in Cadelano et al 2020b): color excess variations as large as δE(B − V ) ∼ 0.51 mag were measured in the relatively small 160 × 160 field of view (FOV) sampled by the adopted data-set. The differential reddening corrected CMD allowed the authors to derive an age of 13 ± 0.5 Gyr.…”

Section: Introductionmentioning

confidence: 99%

Discovery of a double sequence of blue straggler stars in the core-collapsed globular cluster NGC 6256

Cadelano¹,

Ferraro²,

Dalessandro³

et al. 2022

Preprint

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We used a combination of high-resolution optical images acquired with the Hubble Space Telescope and near-IR wide-field data to investigate the stellar density profile and the population of blue straggler star (BSS) in the Galactic globular cluster NGC6256, with the aim of probing its current stage of internal dynamical evolution. We found that the inner stellar density profile significantly deviates from a King model while is well reproduced by a steep cusp with a power-law slope α cusp = −0.89, thus implying that the cluster is currently in the post core-collapse (PCC) phase. This is also confirmed by the very high segregation level of the BSS population measured through the A + rh parameter. We also found that the distribution of BSSs in the color-magnitude diagram is characterized by a collimated blue sequence and a red more sparse component, as already observed in other three PCC clusters. The comparison with appropriate collisional models demonstrates that the vast majority of the BSSs lying along the collimated blue sequence is consistent with a generation of coeval (1 Gyr-old) stars with different masses originated by an event that highly enhanced the collisional rate of the system (i.e. the core collapse). This study confirms that the segregation level of BSSs is a powerful dynamical diagnostic also of star cluster in a very advanced stage of dynamical evolution. Moreover, it pushes forward the possibility of using the morphology of the BSS in the color-magnitude diagram as a tracer of the core-collapse and subsequent dynamical evolutionary phases.

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Digging for Relics of the Past: The Ancient and Obscured Bulge Globular Cluster NGC 6256

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Cited by 27 publications

References 70 publications

A new identity card for the bulge globular cluster NGC 6440 from resolved star counts

A new identity card for the bulge globular cluster NGC 6440 from resolved star counts

Relative Ages of Nine Inner Milky Way Globular Clusters from Proper Motion Cleaned Color-Magnitude Diagrams

Discovery of a double sequence of blue straggler stars in the core-collapsed globular cluster NGC 6256

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